In the manufacture of integrated circuits a finished chip is a quite small, usually rectangular entity with thin-film leads out to the edges from patterned circuitry on the chip. To integrate a chip into a larger circuit scheme it is necessary to connect the thin film-leads to wiring components and conducting traces in the larger scheme. The common circuitry unit for assembly into electronic equipment, such as a home computer, is the familiar printed circuit board (PCB). To be able to mount chips into the circuitry pattern of a PCB, chips are first enclosed in packages in which wire leads connect to the thin-film leads of the chip and protrude from the edges of the package in a usually rectangular pattern. The wire leads are typically round wire. The package typically furnishes several functions, such as protection of the chip from corrosion, abrasion, and shock, and often serves as a heat dissipation device as well.
A chip package furnishes added strength as well for commercial use, and the wire leads are more durable than the thin film leads on the chip itself. The wires typically protrude from the edges of the package in the plane of that flat package and then turn 90 degrees to the plane. This orientation allows the wires to be inserted into pre-prepared holes in a circuit board, in contact with traces on the circuit board to form a pre-planned circuit, and to be soldered or cemented to the traces, with the package describing a low profile.
In the manufacture of packaged chips, it is necessary to test the chips and the integrity of the connections of the chips to the packages. An industry devoted to apparatus for testing and sorting packages automatically has grown up around the high volume production of integrated circuit packages for circuit boards. The machines are generally termed automatic test handler (ATH) machines. These machines bank a supply of packages to be tested, typically with the packages contained in pockets of formed plastic trays. They handle the trays and use pick and place devices to pick packages from tray pockets and place the packages on test equipment. They apply the leads of the packages to test heads, typically inserting the wire leads into sockets in the test heads, which simulate the arrangement of holes on a circuit board, and a test unit performs electrical test on the chip and package. The machines unplug the packages after test and replace the packages in either the original or other trays, sorted according to the results of the test.
More recently circuit boards have been developed that have mounting pads instead of holes for mounting leads from chip packages. These boards are used with special chip packages called surface mount devices (SMDs), and leads from the packages are soldered or cemented to pad surfaces. The boards have several advantages, such as the fact that they are generally less expensive to make, having no holes. The holes have typically required conductive material in the hole, which has been difficult to accomplish, especially as holes have become smaller and more densly located.
FIG. 1 shows a rectangular SMD 11 with a number of leads from each of the four edges. The device of FIG. 1 shows 16 leads along each edge. The number of leads for such devices varies in the industry. Devices with a total of 44, 80, and 100 or more leads are typical. The leads 15 extend from the edges of enclosure 13 in the plane of the generally flat device, turn 90 degrees to provide for height so the deive may be mounted above a circuit board, then turn again 90 degrees leading away from the SMD, forming flattened feet for mounting to pads on a PCB. The SMB of FIG. 1 is known as a Quad Flat Pack (QFP) in the art, and is a geometry that has been favored by Japanese manufacturers. The geometry of the leads of the QFP shown for attachment to circuit boards designed for SMDs is called a gull wing design in the art. Other SMDs have leads in somewhat different shapes, but also generally forming a surface at each lead to contact a surface of a mounting pad on a PCB. The Quad package of FIG. 1 is about 15 mm. square, although there are other sizes for packaging different chips with different numbers of leads.
Automated handlers for device packages with leads that insert into holes in PCBs and can be inserted into test sockets in a similar manner are not useful for SMD packs with gull wing leads or with leads of other shapes that relay on a mounting surface to mate with the surface of a pad. The leads with flat contact surfaces cannot be inserted into sockets designed to straighten and position the leads, called pin strighteners, nor can they be inserted into conventional test sockets, which accomodate round-wire leads. The leads from SMDs have to be presented to test leads making surface contact, and urged into the array of test leads so all of the package leads make contact with test leads. One difficulty with this requirement is that the package edges are unreliable indicators of the location of the leads, and another is that the leads are not all in exactly the same plane at the contact surfaces.
To test SMDs with flat surface leads, such as gull wing leads, manual insert test sockets have been developed. These are test boxes with hinged lids having contacts on the inside to align with SMD leads and pin leads on the back that may be attached to circuit test boards, for example by soldering. FIG. 2 is a perspective view of a typical manual insert test socket 17. The test socket has a base 19 and a lid 21. The base has rows of pins such as row 23 which are arranged in a pattern to present surfaces to contact the gull wing leads of SMD 11. In the socket of FIG. 2 there are four such rows to correspond to the four rows of leads of SMD 11, although for other SMDs the arrangement would be different.
Lid 21 is hinged to the base and a spring 25 tends to hold the lid in the open position shown. To initiate a test an operator places an SMD in the socket so the leads rest on the socket leads. The handling is typically done with a vacuum wand (not shown). The socket base has guide posts 27, 29, 31 and 33 positioned at the corners of the test lead array to guide the SMD into place. The guide posts are replaces to that the angled edges of the guide posts contact the edges of the rows of leads on the SMD rather than any part of the enclosure from which the leads protrude. For example, edge 35 of guide post 31 contacts edge 31 of one of the rows of leads of the SMD. This arrangement avoids the use of any part of the enclosure to guide the SMD leads into contact with the socket test leads.
When an SMD is in place, the operator closes the lid against spring 25. The lid has protruding ridges 37, 39, 41 and 43 that align in the closed position with the four rows of test leads. For example, ridge 37 aligns with row 23 in the closed position. When the operator closes the lid, a spring-loaded latch 45 pivoted in the lid engages a catch 47 built in to the base to hold the lid closed over the SMD in the socket while a test is accomplished. Ridges 37, 39, 41 and 43 urge the gull wing leads of the SMD against the test leads of the socket, and no other part of the SMD is typically contacted. The base of the test socket has pins from the lower surface (not shown) to plug into or otherwise attach to a test board, which has all the circuitry, switching elements, power supplies and the like that are needed to adequately test the SMD.
Although manual insert test sockets allow SMDs to be tested, there are still some serious drawbacks. One drawback is the fact that the operations are manual, and therefore expensive. Another is that it is difficult for an operator to place an SMD in a manual socket keeping the SMD and the socket relatively parallel. A frequent result is that an SMD is inserted in a slightly cocked position, so the leads are not resting on the test leads on all four rows, so when the lid iis closed, the SMD leads are damaged. Often the damage is so severe that straightening is impractical, and the SMD has to be discarded.
What is needed is an apparatus that allows SMDs to be handled automatically, placed to and retreived from a test socket, so that many more tests may be done at a higher rate without manual intervention, also avoiding human placement errors that damage the SMDs. Such an apparatus also needs to be capable of manipulating tray carriers with pockets to position individual SMDs for placement, and to sort tested SMDs according to test results, placing tested devices in different trays.